The major focus of this research group is the study of responses to genotoxic stress in mammalian cells. This has included the cloning and characterization of a variety of DNA-damage-inducible (DDI) genes. Studies have involved mammalian genes such as the gadd genes, beta-polymerase, metallothionein, and ubiquitin. Understanding the role of DNA-damage responses in determining the cellular sensitivity to cytotoxic agents. such as used in cancer therapy, is a major objective: efforts include DDI gene expression in drug-resistant tumor cells (formerly project Z01 CM 07187-02 LMPH). An important response to genotoxic stress in all cells are delays in cell cycle progression which are induced by DNA damage. Such delays can have a protective effect since mutants lacking growth arrest responses are hypersensitive to certain DNA-damaging agents. These delays are mediated by various genes and probably include the gadd genes which are both DDI and growth-arrest inducible and which were cloned in this laboratory. The major portions of this project focus on: 1) the study of the expression of these genes and characterization of the cDNA clones for these five genes: 2) the regulation of these genes with particular emphasis on gadd45; 3) the characterization of the gadd proteins with the development of high-affinity antibodies; 4) attempts to elucidate the function of these genes using expression vectors and antisense approaches; 5) the use of a transgenic mouse models to study the roles of these genes in vivo. Of particular interest is our recent finding that the induction of the human GADD45 gene by certain DNA-damaging agents is mediated by the p53 tumor suppressor. In collaboration with M. Kastan and B. Vogelstein, we have found that this gene is only induced by x rays in cells with a p53 wt phenotype. In addition. both the human and hamster gadd45 genes contain a conserved p53 consensus sequence which strongly binds p53 protein. These findings are the first demonstration of a cellular gene whose activation is dependent on p53. This may have important implications in cancer therapy considering that approximately two thirds of human tumors lack normal(wt) p53 function.